“This type of research will inform future health regulations”: How intrauterine exposure to nanoplastics alters brain development in mice

(Photo provided by Nikita Harvey)

“Analysis of brain structure showed brain differences in mice exposed to nanoplastics. These differences were in areas important for motor function, learning and memory, and physiological functions. Several of these changes were different between females and males.” ~Nikita Harvey

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*In the following article, TS refers to The Synapse and NH refers to Nikita Harvey;

TS: Could you briefly introduce yourself, your supervisor, the topic of your thesis, and the field it contributes to? 

NH: My name is Nikita Harvey and I am currently a Master of Science student in chemistry at Memorial University of Newfoundland. I completed my undergraduate honours thesis with Dr. Lindsay Cahill, who is a biophysical chemist who studies neurodegenerative, neurodevelopmental, and pregnancy disorders in mouse models. 

My honours project was about the impact of ingested nanoplastics (i.e. plastic that have been broken down in the environment into small particles) on the development and brain structure of mice. This work contributes to the fields of biophysical chemistry and environmental toxicology. 

TS: What is the inspiration for your study, and the research question?

NH: This study was inspired by the growing concern about the potential impacts of nanoplastics (NPs) on human health. The worldwide use of plastics has resulted in an accumulation of plastics in the environment that break down into microplastics and nanoplastics. These plastics can be ingested by humans and potentially accumulate in tissues and organs. 

A recent study found that microplastics were discovered in the placentas of healthy women. This raised the concern that exposure to plastics may have an impact on pregnancy and fetal development. My project served to study this further by assessing whether mice offspring from mothers exposed to nanoplastics would show behavioural differences and structural brain differences. I was excited to be a part of this study to learn more about the potential impacts of plastic on the developing brain. 

TS: Could you provide a brief summary of the methods/ experimental procedure used in this study? 

NH: This study was conducted with a mouse model, a standard model for human pregnancy.

Twenty pregnant mice were randomly assigned to either a NP-exposed group or a control group, with ten mice in each group. The control group received filtered water, and the NP-exposed group received filtered water infused with a concentration of NPs. 

Once pups from the control group mice and NP-exposed group mice were born, they were tattooed for identification purposes. The pups underwent behavioural testing to determine if maternal NP exposure impacted postnatal growth and developmental milestones. Specifically, we assessed the righting reflex (i.e. whether mice can flip onto their feet after being placed on their back) and the eye-opening test (i.e. how quickly mice open their eyes after birth). These can be considered behavioural markers of brain maturation. 

At day twenty-three, when the mice were considered to be at adolescence, their brain tissue was collected to determine if maternal NP exposure caused structural changes to the brain. 

TS: What are the main results you observed? 

NH: From the behavioural results, there was no significant difference in motor function as measured by the righting reflex test. However, a significant difference was found in the eye-opening test: the males in the NP-exposed group opened their eyes earlier than controls, suggesting abnormal brain maturation. 

Analysis of brain structure showed brain differences in mice exposed to nanoplastics. These differences were in areas important for motor function, learning and memory, and physiological functions. Several of these changes were different between females and males.

The figure below depicts the structural differences in the brains of control and NP-exposed mice. The images have been overlaid with colour maps indicating regions that are structurally larger (hot colors) and structurally smaller (cool colors) in NP-exposed mice. 

(Images of brain structure comparisons in control mice and NP-exposed mice (group effect column). Hot colours indicate regions that are structurally larger in NP-exposed mice, and cool colours indicate regions that are structurally smaller in NP-exposed mice. Figure provided by Nikita Harvey)

TS: What would you consider the most intriguing part of the research process? 

NH: For me, the most intriguing part of the research was the hands-on experience of running behavioural testing. It allowed me to see interesting differences between the study groups in real time. This is what made data analysis so exciting - to see all the research come together, and motivate further research that may close the knowledge gap about the impacts of nanoplastics during pregnancy and early life.

TS: Is there anything else you wish to share about the research experience/ study?

NH: If you are interested in reading more on this project you can do so here: Maternal exposure to polystyrene nanoplastics impacts developmental milestones and brain structure in mouse offspring. It was published last February!

Our group continues to study the effects of microplastics and nanoplastics during pregnancy to explore its impacts on human health. Hopefully, this type of research will inform future health regulations to minimize exposure to plastics. Ψ

Created for The Synapse by Incé Husain.